Typed argument

[alehander92]

Currently gara manages to transform the matches only based on untyped info. I actually like that a lot: it depends on a minimum of knowledge and for the same syntax input it always generates the same output, which is kinda cool.

Still, this has some problems:

• The generated code is full of when which is kinda confusing: we can generate very readable code which helps debugging
• Error reporting could use some help by type info

Let's start using the type info for arg